But @sambazi's comment talks about ISPs doing the blocking.

Yes of course, internet appliances are capable of DNS-blocking whatever their operators tell them to block. This is not news to me, nor to anybody else reading Hacker News.

Also the vendor of this appliance does not classify things as "Extremism". The owner/operator of the appliance does those things. Claiming that "SonicWall is classifying it as Extremism" is like claiming that "Intel marked your email as spam" because your SMTP server uses an Intel CPU.